The present invention relates to electrical connectors and in particular, to a low mating force socket for the acceptance of a multiple spring male twist pin.
Pin and socket connectors are employed in a wide variety of electrical applications, for example, cable connectors, edgeboard connectors, and coaxial cable terminations. In such connectors, one or more pins are arranged on a male connector member and corresponding sockets are arranged on a female connector member. The pins and sockets are dimensioned for cooperative frictional engagement whereby the connector maintains its structural and electrical integrity even after repeated disconnect of the pins from the sockets.
One common form of pin now in use is a "twist pin" which comprises a core of one or more strands formed of, for example, soft copper, surrounded by one or more clusters of beryllium copper spring wire that are helically wound around the core wires. The pin is formed so that the outer wires bulge outwardly. The midsection of the pin has an expanded diameter larger than the inside diameter of the complementary socket. Since the diameter of the expanded cross-section of the pin bundle in its pre-engaged state is greater than the cross-section diameter of the socket, the outer wires of the pin are resiliently compressed to produce a desired contact pressure between the pin and socket when the pin is inserted into the socket. The high degree of resiliency of the socket-engaging wires insures a secure mechanical engagement and a reliable electrical connection as the pin bears against the socket along a substantial interface after insertion into the socket.
In practice, the forces required to engage a given pin and socket are often over 6 ounces of force per contact. While such a force per contact is not significant, per se, it will be appreciated that in a connector employing over a hundred contacts (e.g., over 300 contacts in a whole family of airborne connectors), the overall mating force required to mate the male and female connector members can be very high, even when the contacts have been lubricated. Thus, assembly force limits the number of contacts which can be employed in a connector. Any attempt to alleviate this inconvenience must not result in a reduction in the separation force (i.e., the force needed to separate the pins from their sockets), below a given minimum value, (e.g., 0.5 oz.). Moreover, unless a minimum contact pressure or force is present, the electrical connection across the separatable interface may be compromised.
Efforts to deal with this condition have focused on pin configurations. For example, attempts to solve the problem included the use of coreless pins in which the center or core cable is omitted, use of three cables of four wires, four cables of three wires each, or pins formed of a core of three helically wound wires having 11 or 12 wires helically wound therearound. However, undesirably high engagement forces resulted from each of the aforesaid pin configurations.
Set in the above context, a new approach to the problem of high mating force is required. Normally the socket receiving a twist pin is manufactured with a cylindrical bore having an internal diameter D. The twist pin comprises a compressible spring having a maximum outside diameter greater than D. When inserted into the socket, a controlled amount of spring compression serves to overcome electrical resistance associated with the contact interface by supplying a predetermined contact pressure. Thus, known male sockets have a cylindrical bore wherein all of the active spring members come in contact with the socket wall and start compressing simultaneously.
In contradistinction, the instant invention relates to a connector utilizing a socket wherein the helical nature of the twist pin interacts with localized compression zones to control and reduce mating forces. A socket configured with the circumferentially spaced axially extending compression zones of the instant invention is progressively exposed to the helically arranged springs during the engaging motion.
The three contributing factors exhibited by the connector socket of the instant invention which result in a reduction in engaging force are:
(a) Reduced rub area,
(b) Not all springs are fully compressed because of concomitant arrival at a compression site, and
(c) The sequential loading of the spring members making contact with the compression site during the engaging motion.
Stated in another manner, a substantial reduction of connector mating force is achieved by shaping the socket to reconfigure the surface rub area encountered when a male twist pin is engaged therewith.